Treatment Resistant Depression (TRD) is defined as an inadequate response to at least one antidepressant of adequate dose and duration in patients suffering from major depressive disorder (MDD).
Adequate duration is a minimum of 6 weeks and adequate dose is dependent on the antidepressant prescribed. Inadequate response is generally defined as a failure to achieve full symptom remission. The number of patients who fail to adequately respond to antidepressant therapy is significant. According to the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) trial, only 30% of patients were in remission following 12 weeks of therapy with the selective serotonin receptor inhibitor (SSRI) citalopram. In a review of 163 randomized, double-blind placebo-controlled trials of antidepressant use in MDD conducted by Papakostas and Fava, only 53.4% of patients responded following treatment versus 36.6% of patients on placebo.
Currently, there are few treatments available to persons suffering from TRD. Until recently, the condition has mainly been treated with electroconvulsive therapy. Today, intravenous ketamine is also used but this treatment causes psychotic-like effects which can increase in intensity with prolonged use. New therapies with an improved side effect profile are urgently needed.